Examples of articles which easily deteriorate or degrade under the effect of oxygen include foods, beverages, medicinal products and cosmetics. For the purpose of preventing oxygen oxidation of such articles, thereby storing them for a long term, oxygen absorbents, which remove oxygen within packaging bodies storing these articles, are used.
As the oxygen absorbent, an oxygen absorbent containing an iron powder (hereinafter, referred to also as “iron-based oxygen absorbent”) as a reactive base compound is generally used in view of oxygen-absorbing ability, handling and safety. However, the iron-based oxygen absorbent is responsive to a metal detector and thus it is difficult to inspect a foreign matter contained in packaging bodies containing such an iron-based oxygen absorbent, by using a metal detector. Furthermore, since the packaging bodies containing an iron-based oxygen absorbent have a risk of ignition, they cannot be heated by a microwave oven. Moreover, the oxidation reaction of an iron powder requires water, and thus, an oxygen-absorbing effect is exerted only on a preserve rich in moisture content.
Packaging containers are developed by making the container of a multilayered material having an oxygen-absorbing layer formed of an oxygen-absorbing resin composition containing a thermoplastic resin and an iron-based oxygen absorbent, thereby improving a gas barrier property of the container and providing an oxygen-absorbing function to the container itself (see, for example, Patent Document 1). However, this container has the same problems: since an iron-based oxygen absorbent is responsive to a metal detector, a foreign matter cannot be inspected by using a metal detector; heating cannot be made by a microwave oven; and an effect is only exerted on a preserve rich in moisture content. In addition, the container has a problem of opacity, leading to insufficient visibility of content.
In the aforementioned circumstances, it has been desired to develop an oxygen absorbent containing an organic substance as a reactive base compound in place of an iron-based oxygen absorbent. Up to present, as the oxygen absorbent containing an organic substance as a reactive base compound, for example, an oxygen absorbent containing ascorbic acid as a base compound is known (see, for example, Patent Document 2).
In the meantime, an oxygen-absorbing resin composition composed of a resin and a transition metal catalyst is known. For example, a resin composition composed of a polyamide as an oxidizable organic component (in particular, a xylylene group-containing polyamide) and a transition metal catalyst, is known (see, for example, Patent Document 3). In Patent Document 3, articles obtained by molding a resin composition, such as an oxygen absorbent, a packaging material and a multilayer laminate film for packaging are also exemplified.
As an oxygen-absorbing resin composition requiring no moisture content for absorbing oxygen, an oxygen-absorbing resin composition composed of a resin having a carbon-carbon unsaturated bond and a transition metal catalyst, is known (see, for example, Patent Document 4).
As a composition for trapping oxygen, a composition composed of a polymer containing a substituted cyclohexene ring or a low molecular-weight substance bound with the cyclohexene ring and a transition metal is known (see, for example, Patent Document 5).